How much can you store on that ipod thing?

*This is a question that a lot of people ask. While it might seem like a dumb question to a lot of advanced users, not everyone is familiar with how the digital audio technology works, and to fuel that fire the resellers and manufacturers often list an approximate number of songs for various players- with very small footnotes clarifying the specs of the files used. While technically accurate, it’s still a fair bit misleading as the people who would ask for the number of songs instead of capacity in the first place are those that won’t know what bitrate or any of that stuff is. Read on to get a quick introduction to MP3 player capacity.
Digital storage 101

When moving up from analog storage media and even CDs you have to let go of the old “it can hold X minutes” way of thinking. Digital storage doesn’t concern itself with how long a song is or how many songs there are, because it’s all digital- meaning there’s no ridges in an LP or anything like that, it’s simply stored as ones and zeros. This might be hard to understand, but think of it like a printed photo; it’s not really a single piece of anything, it’s a piece of paper with millions and millions of very small ink dots printed on it, which to human eyes look like a complete, sharp and clear picture. Digital storage works somewhat the same way, it’s all billions upon billions of ones and zeros that are interpreted by a computer, MP3 player or some other kind of electronic device to be a song, a picture, a document, or anything. Digital storage is measured in bytes, like a printed photo could be measured in number of ink dots. Since there are so many “ink dots”, it’s measured most commonly in millions or billions. One MB, or Megabyte, is one million bytes. One GB, Gigabyte, is one billion bytes. MP3 players these days are measured in GB, so that’s the capacity that is always listed in the player specs.

One thing to be aware of is that there are different ways of counting one GB. Manufacturers of MP3 players use 1000 bytes per kilobyte, 1000 kilobytes per megabyte, and 1000 megabytes per gigabyte- a total of exactly 1 billion. Computers however measure it as 1024 bytes per kilobyte, 1024 kilobytes per megabyte, and 1024 megabytes per gigabyte. The reason isn’t important, but this is how it is. This totals to 1073741824 bytes, or 1,07 billion. Since the computer calculates a gigabyte differently than the MP3 player manufacturer, a 1GB mp3 player plugged into a computer will show up as having a capacity of 931MB. For every extra GB of capacity on the player, it will appear to have lost 69MB for no apparent reason. This might not seem like much, but it does mean that a 16GB player will show to have only 14,9GB of storage when plugged into a computer. Since the system of 1024 instead of 1000 is technically the correct one in the computer industry, this is somewhat of a fraud from the manufacturer’s side since they aren’t really that good at informing people about this. A person might buy a 32GB player for their 31GB music collection and find that the player only has 29,8GB of storage. Unfortunately it’s just something you have to live with and be aware of.


Bitrates
There are a lot of factors that affect quality of audio files,  However, the only thing that affects the size of the files is the bitrate of the music files. Bitrate is put simply the amount of bytes used per second to store the audio. To go back to the photo metaphor, it’s the amount of ink dots used to produce the photos. The more ink dots, the more detailed the photo. Bitrates are always numbers easily divided by 8 (again for reasons that aren’t important). 8, 16, 32, 64, 128, 192, 256 and 320 are the most common ones, though anything below 128 is mostly used for speech (audio books, voice recording). These numbers are in bits, not bytes, and 1 byte equals 8 bits. That means that 320kbps (kilobits per second) is the same as 40kBps (kilobytes per second). It’s a bit backwards to use bits instead of bytes, and many manufacturers use the wrong abbreviation for the capacity. In some extreme cases- particularly for Chinese players and other cheap, non-trustworthy manufacturers- they intentionally use bits in the listing of capacity as it will allow them to sell low capacity players as seemingly high capacity ones. Think about it; if you saw a player listed with 16gb priced at $30 it would be a bargain. However, since gb is technically gigabits (capitol B is used for bytes) you’re actually buying a player with 2GB capacity.

MP3 is the most common format, and goes up to 320kbps. Lossless formats and higher capacity formats use higher bitrates, but for the sake of simplicity I’ll concentrate on MP3 bitrates. Other formats and quality issues of various formats are covered in the audio format guide linked to above. There’s also the CBR vs VBR aspect to keep in mind; constant bitrate vs variable bitrate. Variable bitrate basically means that where the music is complex and detailed, higher bitrate is used, while where the music is not so (like where there is silence) it doesn’t use bitrates that high. Back to the photo metaphor, you can think of it like using fewer ink dots to print a clear blue sky than to print a human face, because a human face is much more complex and has more detail. Another way of thinking about it is vacuum packaging instead of big cardboard boxes. Variable bitrate is therefore usually preferred over constant bitrates because it takes up less space (used fewer “ink dots”) while maintaining a higher quality than if you used constant bitrate. Variable bitrate is usually listed with average bitrates. While the amount of difference is a touchy subject for some people, MP3 files are generally considered to sound about the same between 320kbps constant bitrate and 192kbps average bitrate. The latter takes a lot less space because it doesn’t “add details to the sky”.


Many manufacturers claim that 128kbps CBR MP3 is “CD quality”, because it suits them well- low quality used to calculate number of songs means an impressive number of songs the player can hold. In reality, 128kbps is frowned upon by most people- especially when it’s constant bitrate. If you buy tracks from the net, you’ll most likely have either 256kbps CBR or 320kbps VBR files, while bitrates for files from “other places” vary greatly.


So, how much?  This might seem like a lot of info to answer something as simple as how many songs an MP3 player can hold, but there’s a reason why people who know their business sigh when that question is asked. Bitrates, as described above, tells you how much space a song will take up per second. Naturally, the total amount of space equals the bitrate times the duration of the song. On a CD, cassette etc the length was the only thing that mattered, but with digital audio it’s the product of the bitrate and the duration. This is another field where manufacturers cheat, often using 3 minutes or less as the average length of a track when they calculate number of songs. Nice way to cheat people, making it appear like the player can hold more songs than it probably will in real life. As an example, one of the music software applications I use currently holds 45.6 hours of music, which is 725 tracks. That means an average of 3.8 minutes per song, which is probably lower than the average as I have a lot of tracks that are shorter than normal. Depending on what artists you listen to, your average might be 3 minutes or it might be 6 minutes- no-one but you can know. This, combined with the fact that bitrate might vary a lot between files, makes it hard to give a straight number for how many songs a player can hold. The easiest is to just see how big your music collection is and then find a player that can hold it, correcting for the 1024/1000 issue by multiplying the player capacity by 0.931.

Wrap up...

There are a lot of things that end up deciding the number of songs an MP3 player can hold, simply because “number of songs” isn’t a unit of measurement that has any meaning in the digital world. Manufacturers and stores list somewhat random numbers that doesn’t mean much to people because explaining it all would take as much time as this article has taken you to read, and it might still not make much sense to some people. It is however important to understand the concepts behind the capacity of an MP3 player both to not be fooled by listed numbers and also to find the capacity you need. This article doesn’t even touch on video, which is a chapter by itself in the book of capacity, but the same concept with bitrates apply- though bitrate is more hidden in the world of video. Hopefully these charts and this explanation will give some indication of what’s awaiting you when you buy a new player, but remember: there is no sensible unit of measurement for audio capacity.

*this article stole from http://www.anythingbutipod.com/